Pollination and Fertilisation (5) Flashcards
(28 cards)
What is pollination?
Pollination is the transfer of pollen from an anther to a stigma, thereby enabling fertilisation and reproduction.
What happens when the anther is mature?
When the anther is mature it splits open and discharges the pollen. The pollen is then carried to the stigma by various natural means, the most common being wind and insects.
In plant breeding, pollination is carefully controlled by ____.
humans
What are the two kinds of pollination?
There are two kinds of pollen transfer – cross-pollination and self- pollination.
What is cross-pollination?
In cross-pollination the pollen is transferred from the anther of a flower of one plant to the stigma of a flower of another plant, of the same species. This type of pollination will result in genetic variation in the offspring.
what is self-pollination?
In self-pollination the pollen is transferred from the anther to the stigma of the same flower or to another flower on the same plant. This type of pollination will not result in genetic variation in the offspring.
How can self-pollination be prevented in nature? (3)
− In bisexual flowers the anthers and stigmas ripen at different times. Most commonly the anthers ripen first. −Flowers are unisexual, they therefore cannot pollinate themselves.
− The stigma is positioned above the anthers.
How can self-pollination be prevented by plant breeders?
Plant breeders will remove anthers to prevent self-pollination.
What is fertilisation?
Fertilisation is the joining of two haploid cells, the male gamete and female gamete, to form a diploid zygote. The zygote develops by mitosis into the adult plant.
When does fertilisation take place in flowering plants?
After pollination. After the pollen grain lands on the stigma it develops a pollen tube which grows along the style and into the ovule. The pollen tube carries the male gamete. Once the gamete enters the ovule fertilisation can occur. After fertilisation the development of the embryo and the seed can begin.
How is a seed formed after fertilisation? (3)
• the zygote divides numerous times by mitosis and develops into an embryo consisting of: −cotyledons or seed leaves. The cotyledons often take food from the parent plant which they store for future use.
−a radical (embryonic root)
−a plumule (embryonic shoot).
• the rest of the ovule develops into endosperm tissue. This is the stored food, e.g. starch, protein or oil.
• the outer covering of the ovule thickens and hardens, forming the seed coat or testa. It saves the seed from being damaged as well as preventing the entry of bacteria and fungi.
How is a fruit formed?
While a seed is being formed the ovary is also growing. It is now called a fruit. Fruit formation happens in different ways in different plants
What are the functions of fruit?
- They contain and protect the seeds.
2. Fruits help to disperse the seeds from the parent plant
Of the approximate 75 000 species of edible plants 7 000 are used for food by humans. Humans have domesticated wild plants for their use for the last 9 000 to 11 000 years. Domestication lead to: (2)
- great phenotypic changes, (and altered genotypes) resulting in vastly improved food crops.
- new varieties developing.
Today, all our principal food crops come from domesticated varieties. Most of the ____ involved cereals, i.e. wheat, maize and rice.
domestication
Define wild plants.
plants that grow in nature without the aid of humans. Very few wild plants are now used as food sources.
Domestication involved skilful breeding. The breeders used ____ that existed in plant species and also the variation that arose from sexual reproduction to asexually or sexually _____ the food crops further.
variation
improve
What does asexual reproduction cover?
Asexual reproduction covers all those modes of the reproduction of plants where normal gamete formation and fertilisation does not take place.
What are the asexual methods to improve crops? (4)
Techniques include:
- division,
- grafting, using
- storage organs (bulbs, corms, tubers and rhizomes)
- cuttings.
Why is asexual reproduction good in crop production?
While the basic feature of asexual reproduction is genetic stability with no variation in the offspring a mutation could have produced a plant with a new superior trait. For example a crop plant could have produced bigger seeds, fruits or tubers. If these plants were then reproduced by asexual means more plants with the superior trait could have been grown. With repeated selection and elimination of plants without the superior trait the food crop would eventually have consisted entirely of plants with the superior trait. In this way the particular crop would have been improved by asexual means.
What is grafting?
Grafting is a technique whereby tissues from one plant are inserted into those of another so that the two sets join together.
Explain the process of grafting. (2)
- One plant is selected for its roots. This is called the rootstock. Rootstocks with good traits, e.g. resistance to certain pests and diseases and/or the ability to grow in difficult soil conditions would have been used.
- The other plant is chosen for its superior fruits (larger and improved yield) and is called the scion. As the scion contains the superior traits for food production the mature plant would be more productive. Further scions would be cut from this plant for further grafting resulting in an overall improved crop
True or false
Grafting an outdated process.
False. Grafting has been practiced for thousands of years to improve crops, particularly fruit tree e.g. apples, pears. It is still today used in asexual propagation of certain commercially grown food crop plants, e.g. grapes and avocado pears.
True or false
Plant breeders made use of sexual reproduction to improve crops as well.
True. Over time breeders also used sexual reproduction to improve their crops. The plants originating from sexual reproduction were often quite different from their parents and from each other. Some of these differences were beneficial traits that would improve the food crop. Such traits were larger yield, larger seed, tuber and fruit size, resistance to pests and/or disease and being able to grow in poorer soil.
